Archived - Mac OS X: Using Disk Copy disk image files
You may use Disk Copy disk image (.dmg, .img) files and self-mounting disk image (.smi) files in Mac OS X.
This document applies to Mac OS X 10.0 through 10.2.8.
There are two common types of disk image files produced by Apple software: Disk Copy and self-mounting. These instructions may not apply to disk image files created by third-party software.
Disk Copy Disk Image Files
Files of this type normally have the filename extension ".img". Their icon looks like a picture of a hard disk printed on a piece of white paper with one corner folded down:
Disk Copy is included with Mac OS X, and can open disk image files, which means it can make them appear on the desktop or in the Finder as disks. When you download a file of this type, Disk Copy may open automatically, and the opened disk image file may appear on the desktop as a plain, white "volume" icon.
Self-Mounting Disk Image Files
Files of this type normally have the filename extension ".smi". Generally, you can open this type of file by double-clicking its icon. You don't need to open it with the Disk Copy application. However, if the self-mounting disk image file was intended to be used only with Mac OS 9, the Disk Copy application must be installed in the Utilities folder if you want to open it in Mac OS X. The icon for a self-mounting disk image file looks like a blue floppy disk on top of a white diamond:
In some cases, the self-mounting disk image file may temporarily appear with a "blank papers" icon:
How to use a Disk Copy disk image file
To use a disk image file, double-click the file's icon. (It has a filename extension of .img, .smi, or .dmg.)
When it is opened, a new icon representing the disk (or folder) from which the disk image file was created appears on your desktop and in the Finder. It may appear as a plain white volume (as mentioned above) or with a custom icon. This icon remains available until you "eject" it or restart the computer. You may eject a disk image by dragging its icon to the Trash.
Depending on the disk image file, you may notice that the Classic environment and a Classic-compatible version of StuffIt Expander decompresses it. This may only occur if the image file was compressed with an earlier version of Aladdin software and has a ".bin" filename extension. Regardless, once the image file is decompressed and opened, it should appear with one of the above icons, and you should be able to use it.
What's the difference between .img and .dmg disk images?
They are similar, and you can use either with Mac OS X. One difference is .dmg disk images can be formatted in one of these formats: Mac OS Extended (HFS Plus), Mac OS Extended Journaled, Mac OS Standard (HFS), UFS, or MS-DOS. While .img disk images can be formatted as: Mac OS Extended (HFS Plus), Mac OS Standard (HFS), MS-DOS, ProDOS, or Universal Disk Format.
If these steps do not work, or if the disk image contains an installer application that does not work, see "Mac OS: Disk Image File Does Not Open With Disk Copy". If this works, you may need to associate the disk image file with this version of Disk Copy. To do that, use the solution found in "Mac OS X: Double-Clicking a File Opens the Wrong Application".
Contents of a disk image don't open if the disk image file isn't opened
Files or applications stored in a disk image file do not work unless you open the disk image file first. For example, if you drag an application icon from a disk image to the Dock, the application will not open unless you first open the disk image file. You may want to consider copying the contents of the disk image to your hard disk before adding any of its contents to the Dock.